This five-year project proposes an innovative study of a neglected issue in religious studies: the production of comparative knowledge of Judaism in the early academic study of religion. In late 19th century Europe this study – referred to as the ‘science’ or ‘history of religions’ – used comparative-historical methods to replace theological accounts of divine revelation with secular knowledge of religion. Although Judaism was a popular subject of focus among historians of religions, their comparative theories on its origins and history have yet to be examined systematically. It remains unclear whether Judaism was seen as commensurable with religions such as Christianity, Islam, Buddhism, Hinduism, or the indigenous religions of, e.g., Africa or Australia. This project has two main objectives: (1) to investigate the ideas about Judaism held by both Jewish and non-Jewish European historians of religions, set against the historical backgrounds of the widespread othering of non-Christian, non-Western, and non-European peoples, and that of rising antisemitism across Europe; and (2) to study these ideas’ circulation in national and international networks of scholarly correspondence and their instrumentalization as mechanisms of social inclusion and exclusion. In order to realize these aims, this project will introduce two important innovations in the history of religious studies: it will unlock a corpus of hitherto underexplored correspondence, which will be studied in relation to publications, and develop a multidisciplinary analytical framework of historiographical, historical-cultural, and sociological approaches.